Australia: The Land Where Time Began
Climate Swings of the Pleistocene in Australia
Over the last 2.6 million years the fluctuations of the climate have had a profound effect on the Australian continent, in particular on the surface water and the groundwater. The rivers of Australia, as well as the lakes and dunefields, have been greatly affected by the alternating nature of the climate over the last 300,000 years, swinging from dry periods to wet and back again. There were periods in the last 2 interglacials when fluvial conditions dominated that allowed large sand loads in rivers in the Simpson Desert, as well as southeast Australia. White describes the central Australian palaeochannels as 'highly competent sand-load rivers during the last interglacial'. 110,000 years ago was the peak of their fluvial activity, behind world temperature and sea level maxima by about 5,000-10,000 years.
Following this wet period, aridity spread towards the margins of the continent, the spread of aridity peaking at the last glacial maximum. Between about 55,000 and 35,000 BP a wet phase, that was less widespread, has been associated with high sea levels and activity of palaeochannels in southeastern Australia. The sedimentary record in rivers and lakes, and the time of dune formation, documents the spread of aridity from central Australia towards the coast across the continent.
The peak of river activity on the Riverine Plain occurred from about 90,000-85,000 BP. On the Nepean River, at Cranbrook Terrace, nearer the coast, river activity peaked at about 80,000 BP and the coastal rivers continued their high level of activity until about 70,000 BP.
In the Eyre Basin, dunes began to form about 95,000 BP during the last interglacial. Dunes began to form on the areas bordering streams and lakes of the Riverine Plain, that is about half way between the Centre and the coast, from about 70,000-50,000 BP. Dunes began forming in the Lake George Basin, close to the coast, and the Shoalhaven Basin, on the coast, during the last glacial maximum about 20,000 BP. According to White, at this time, the peak of the last glacial, it has been estimated that Australia received half the present rainfall and the winds were double their present strength, up to 80 % of the continent being covered by wind-blown sand. It was at this time that the dunefields reached their present state. Also at this time much of the Murray Basin was a salt-sand desert.
Over the last 10,000 years, the Holocene, there have been variations of temperature and sea level. At about 9,000 BP the temperatures were higher than at the present in Australia, and there was increased rainfall. The highest the sea levels reached in the Holocene was from about 7,500-6,000 BP. Since then the sea levels have been approximately stable, though the fact that some low-lying islands are shrinking, with the sea encroaching on villages that have existed on the coast for many years suggests things might be changing.
|Author: M.H.Monroe Email: email@example.com Sources & Further reading